Blitz - WPT: background-position-x-computed.html

wpt / css / css-backgrounds / parsing / background-position-x-computed.html

Data from commit:
a50cb89 wpt: run reference-named files which are themselves tests (#836) (2026-09-03)

Subtest	Status	Message
Property background-position-x value 'center'	PASS
Property background-position-x value 'left'	PASS
Property background-position-x value 'right'	PASS
Property background-position-x value 'x-start'	FAIL	assert_true: 'x-start' is a supported value for background-position-x. expected true got false
Property background-position-x value 'x-end'	FAIL	assert_true: 'x-end' is a supported value for background-position-x. expected true got false
Property background-position-x value '-20%'	PASS
Property background-position-x value '10px'	PASS
Property background-position-x value '0.5em'	PASS
Property background-position-x value 'calc(10px - 0.5em)'	PASS
Property background-position-x value 'left -20%'	PASS
Property background-position-x value 'right -10px'	PASS
Property background-position-x value '-20%, 10px'	PASS
Property background-position-x value 'center, left, right'	PASS
Property background-position-x value '0.5em, x-start, x-end'	FAIL	assert_true: '0.5em, x-start, x-end' is a supported value for background-position-x. expected true got false
Property background-position-x value 'calc(10px - 0.5em), -20%, 10px'	PASS
Property background-position-x value 'calc(10px - 0.5em), left -20%, right 10px'	PASS
Property background-position-x value 'center' multiple base values	PASS
Property background-position-x value 'center, left' multiple base values	PASS
Property background-position-x value 'center, left, right' multiple base values	PASS

Enable JavaScript in test iframe

/css/css-backgrounds/parsing/background-position-x-computed.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>CSS Backgrounds and Borders Module Level 4: getComputedStyle().backgroundPositionX</title>
<link rel="help" href="https://drafts.csswg.org/css-backgrounds-4/#propdef-background-position-x">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/css/support/computed-testcommon.js"></script>
<style>
  #target {
    font-size: 40px;
  }
</style>
</head>
<body>
<div id="target"></div>
<script>
test_computed_value("background-position-x", "center", "50%");
test_computed_value("background-position-x", "left", "0%");
test_computed_value("background-position-x", "right", "100%");
test_computed_value("background-position-x", "x-start");
test_computed_value("background-position-x", "x-end");
test_computed_value("background-position-x", "-20%");
test_computed_value("background-position-x", "10px");
test_computed_value("background-position-x", "0.5em", "20px");
test_computed_value("background-position-x", "calc(10px - 0.5em)", "-10px");
test_computed_value("background-position-x", "left -20%", "-20%");
test_computed_value("background-position-x", "right -10px", "calc(100% + 10px)");
test_computed_value("background-position-x", "-20%, 10px", "-20%, 10px");
test_computed_value("background-position-x", "center, left, right", "50%, 0%, 100%");
test_computed_value("background-position-x", "0.5em, x-start, x-end", "20px, 0%, 100%");
test_computed_value("background-position-x", "calc(10px - 0.5em), -20%, 10px", "-10px, -20%, 10px");
test_computed_value("background-position-x", "calc(10px - 0.5em), left -20%, right 10px", "-10px, -20%, calc(100% - 10px)");

document.getElementById("target").style['background-image'] = "none, none";
test_computed_value("background-position-x", "center", "50%", "multiple base values");
test_computed_value("background-position-x", "center, left", "50%, 0%", "multiple base values");
test_computed_value("background-position-x", "center, left, right", "50%, 0%, 100%", "multiple base values");
</script>
</body>
</html>